1. Field of the Invention
The present invention relates generally to methods and apparatus for communication for well site operations. It is particularly useful for well site communications in which a reeled or spooled conveyance is used.
2. Description of the Related Art
On many occasions in well site operations, and for a variety of purposes it is desired to convey tools, sensors, or other apparatuses into a wellbore. Reeled or spooled conveyances, such as coiled tubing, wireline, and slickline commonly are used. Coiled tubing is useful particularly for conveying such devices in highly deviated or horizontal wells. While spooled conveyances offer several operational advantages in handling, transport, and deployment, the transition between a stationary surface system and the rotating reeled or spooled conveyances can be difficult. Typically collectors disposed on the reel or spool plus associated wiring are used to accommodate this transition to connect the reeled conveyance to surface systems. This wiring can be physically cumbersome in a work location. In addition, collectors may become unreliable or break.
A typical configuration for the surface handling equipment for coiled tubing is shown generally in FIG. 1. The surface handling equipment includes an injector system 20 on supports 29 and coiled tubing reel assembly 10 on reel stand 12, flat, trailer, truck or other such device. The tubing is deployed into or pulled out of the well using an injector head 19. The equipment further includes a levelwind mechanism 13 for guiding coiled tubing 15 on and off the reel 10. The coiled tubing 15 passes over tubing guide arch 18 which provides a bending radius for moving the tubing into a vertical orientation for injection through wellhead devices into the wellbore. The tubing passes from tubing guide arch 18 into the injector head 19 which grippingly engages the tubing and pushes it into the well. A stripper assembly 21 under the injector maintains a dynamic and static seal around the tubing to hold well pressure within the well as the tubing passes into the wellhead devices which are under well pressure. The coiled tubing then moves through a blowout preventor (BOP) stack 23, a flow tee 25 and wellhead master valve or tree valve 27. A quick connect fitting is placed between the BOP and the stripper above.
When coiled tubing 15 disposed on a coiled tubing reel 10 is deployed into or retrieved from a borehole 8, the coiled tubing reel 10 rotates. In typical communications in coiled tubing operations as shown in FIG. 2, a collector 30 is fitted to the reel 10 and used to connect and provide communication between the downhole system and the surface data acquisition equipment 36. Commonly the collector 30 has a slip ring configuration that maintains the power and signal connection regardless of reel orientation. The communication element may be truncated in a feed-through pressure bulkhead 32 with wired telemetry signal path 34 continuing through the reel axle and out the collector ring. In coiled tubing operations, the signal path 34 commonly exits through the reel axle on the opposite side from the fluid swivel. From the reel or spool, the signal path 34 is connected to a surface data acquisition system 36. In this way, data signals may be passed uphole to or control signals may be passed downhole from the borehole communication element through the collector ring on the reel assembly to the surface data acquisition components. This prior art method of establishing communication in coiled tubing operations requires a physical connection, such as wiring, for the signal path. This physical connection can be disadvantageous as it restricts the possible spatial configuration of components, limits placement of equipment, and adds a wire line to be avoided by personnel during well site operations. In addition the use of a collector 30 adds expense to the system and requires maintenance.
A typical coiled tubing communication system comprises a surface acquisition system linked via a downhole telemetry system to a downhole acquisition system in which information is sensed downhole. Various methods of downhole telemetry to link downhole acquisition systems to surface acquisition systems are known and include mud pulsing, mechanically generated signal events, wireline cables, and slickline. Often during wellbore operations it is beneficial to have real-time knowledge of the actual downhole conditions. One method of accomplishing this in coiled tubing operations is to dispose a communication element, such as wireline, in the coiled tubing. Wireline provides the functionality of permitting communication in both uphole (e.g. sensed data from borehole apparatuses) and in downhole (e.g. operational commands) direction. Typically the wireline communication element is linked to a surface acquisition system such as a wireline truck.
While providing wireline in cable may permit real-time transmission of downhole data to the surface, using wireline inside coiled tubing presents some disadvantages. It reduces the cross-sectional area available for fluid flow in the tube. It incurs a large friction against the fluid flow owing to the relatively large diameter of the wireline compared to the fluid flow path within the coiled tubing, as well as the typical multi-stranded nature of the wireline. As a result, large friction and turbulence factors may be introduced. Another difficulty with electrical cables is the weight of the cable; it can increase the system weight by up to 25%, making it difficult to manipulate and install in the field.
A system to communicate information about downhole conditions to the surface and surface information downhole is desirable. In particular, a communication system to sense, control and verify the status of the wellbore operations using reeled or spooled conveyance is desirable. While described in the context of a coiled tubing conveyance system, the present invention is well suited for use with any reeled or spooled conveyance system. Thus, a method and apparatus for well bore communication is needed that is capable of transmitting downhole information to the surface and communicating that data to the surface acquisition system in real time without the disadvantages of using a surface collector.